[getdns-users] why do we link libgetdns.so to dlopen?

[W.C.A. Wijngaards]

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Hi Daniel,

On 11/04/2015 11:53 PM, W.C.A. Wijngaards wrote:
> Hi Daniel,
> 
> On 11/04/2015 11:23 PM, Daniel Kahn Gillmor wrote:
>> i noticed that libgetdns.so is being linked against libdl, but i 
>> don't think we're using dlopen or any of the other functions 
>> exported from ldl.
> 
>> fwict, ./configure is adding -ldl because of m4/acx_openssl.m4, 
>> which claims:
> 
>> # openssl engine functionality needs dlopen(). BAKLIBS="$LIBS" 
>> AC_SEARCH_LIBS([dlopen], [dl]) if test "$LIBS" != "$BAKLIBS";
>> then LIBSSL_LIBS="$LIBSSL_LIBS -ldl" fi

Testing that, I see that for getdns and Unbound the patch is safe,
because it is tested (but more properly) in ACX_LIB_SSL.

Best regards, Wouter

> 
>> However, we're not using OpenSSL Engine support directly.  If
>> some library user wants to initialize openssl's engine support,
>> they should be able to do that with OpenSSL itself, and then they
>> should be able to get libcrypto and/or libssl to use libdl
>> directly.
> 
> But that is not how the linker works, I understand you would like
> it to.
> 
> 
>> On some minimal systems, libcrypto and libssl might be built 
>> without engine support at all; in that case, libgetdns is adding
>> a superfluous dependency to the linker.
> 
> Regardless of what calls getdns uses, the dependency of openssl on 
> libdl has to be satisfied for the linker to succeed.
> 
> 
>> I don't know the what the getdns policy is about tweaking the
>> files in m4/, but maybe the following patch can be safely
>> applied?
> 
> No, you cannot safely apply that patch.  The library will not link 
> properly (at compile time or at run time, not sure) for some 
> setups/platforms.  Leaving out -ldl when possible would be a nice 
> patch (that I would also like for unbound and NSD).
> 
> Best regards, Wouter
> 
> 
>> diff --git a/m4/acx_openssl.m4 b/m4/acx_openssl.m4 index 
>> 87507dc..059a670 100644 --- a/m4/acx_openssl.m4 +++ 
>> b/m4/acx_openssl.m4 @@ -95,12 +95,6 @@
>> AC_DEFUN([ACX_SSL_CHECKS], [ fi AC_SUBST(HAVE_SSL)
>> AC_SUBST(RUNTIME_PATH) -	# openssl engine functionality needs
>> dlopen(). -	BAKLIBS="$LIBS" - AC_SEARCH_LIBS([dlopen], [dl]) -	if
>> test "$LIBS" != "$BAKLIBS"; then -		LIBSSL_LIBS="$LIBSSL_LIBS
>> -ldl" -	fi fi AC_CHECK_HEADERS([openssl/ssl.h],,,
>> [AC_INCLUDES_DEFAULT]) AC_CHECK_HEADERS([openssl/err.h],,,
>> [AC_INCLUDES_DEFAULT])
> 
> 
>> wdyt?
> 
>> --dkg _______________________________________________ Users
>> mailing list Users at getdnsapi.net 
>> http://getdnsapi.net/mailman/listinfo/users
> 
> 
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> 

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